The drones were repeatedly shot out of the sky by surface-to-air missiles. Suspending the program effectively blinds observers to numerous cease-fire violations.

By John HudsonJohn Hudson is a senior reporter at Foreign Policy, where he covers diplomacy and national security issues in Washington. He has reported from several geopolitical hotspots, including Ukraine, Pakistan, Malaysia, China, and Georgia. Prior to joining FP, John covered politics and global affairs for the Atlantic magazine’s news blog, the Atlantic Wire. In 2008, he covered the August war between Russia and Georgia from Tbilisi and the breakaway region of Abkhazia. He has appeared on CNN, MSNBC, BBC, C-SPAN, Fox News radio, Al Jazeera, and other broadcast outlets. He has been with the magazine since 2013.

KIEV, Ukraine — The European security organization tasked with monitoring deadly violence between government forces and Russian-backed separatists in eastern Ukraine has lost its most effective surveillance tool in the conflict: long-range unmanned aerial vehicles, or drones.

The long-range drone program was crucial for spotting armed attacks, the stationing of prohibited weapons, and countless other cease-fire violations. But it was nixed two months ago, Foreign Policy has learned, after several of the aircraft were targeted by surface-to-air missiles and military-grade electronic jamming.

“Long-range UAV operations were suspended in August following a series of hostile acts,” said Natacha Rajakovic, a spokeswoman for the Organization for Security and Cooperation in Europe (OSCE), the group authorized by world powers to observe the conflict. “The mission’s UAV strength has been severely undermined.”

The OSCE would not assign responsibility for the drone downings, citing a lack of access to the crash sites. Senior U.S. and Ukrainian officials accused Russian-backed separatists of targeting the UAVs to conceal their actions. Russian officials declined to comment for this report after several requests, but Moscow has repeatedly denied involvement.

The OSCE’s decision to suspend the droneprogram, which has not been previously reported, creates a major blind spot for the organization. It also raises questions about how a cease-fire can ultimately take hold without a capable third party to call out violations.

The long-range drones were often the only way to monitor the most contested and violence-prone areas in Ukraine’s two-year conflict. During the day, unarmed OSCE ground patrols are frequently denied access to hot spots by the warring parties. At night, they are required to decamp to hotels away from the fighting. The OSCE’s Camcopter S-100 drones solved both problems, lurking over restricted areas in the daylight and using infrared cameras to capture violations after sundown.

“The long-range drones were the most important monitors,” a former senior OSCE official told FP. “They catalogued countless cease-fire violations, as well as the stationing and movement of prohibited weaponry.”

But their effectiveness also made them a target for belligerents looking for an edge over opponents without notice.

In May, an S-100 drone flying over rebel-controlled Ozerianivka crashed shortly after spotting a surface-to-air missile system mounted on top of a multi-purpose tracked vehicle. OSCE workers chose not to inspect the site of the crash after being informed by Ukraine’s military and rebel separatists that “the area was mined,” according to an OSCE spot report.

One week later, another S-100 drone was downed while flying over rebel-held Korsun northeast of Donetsk. The day before the crash, the drone spotted an anti-aircraft gun and surface-to-air missile launcher in the area.

Other crashes point to the use of electronic warfare to take down aerial monitoring equipment. On July 25, the OSCE lost all communication with a long-range drone before it plunged to the ground mid-flight. Three days later, OSCE cameras photographed an R-330ZH Zhitel communications jamming system, which is designed and manufactured in Russia, in rebel-held Novohryhorivka near Donetsk.

The former OSCE official said the drones captured images that rebels didn’t want publicized. “The fact that the rebels brought in state-of-the-art electronic jamming equipment attests to the capability of the drones,” said the former official, who spoke on condition of anonymity.

Publicly, OSCE officials maintain that both sides in the Ukraine conflict are responsible for cease-fire violations, though their reports often provide clues to show who’s responsible for a given incident. The organization’s careful diplomatic language is a result of its diverse membership: The 57-nation group includes chief adversaries Ukraine and Russia and makes decisions by consensus.

The group’s mandate is to monitor the conflict, not to keep the peace. Its unarmed monitors, most of them European diplomats, are authorized to record cease-fire violations, escort shipments of humanitarian assistance, and help broker local truces. The group reports dozens to hundreds of cease-fire violations every day, according to the New York Times, patrolling bumpy roads in armored Toyota Land Cruisers.

Though the conflict receives fewer headlines now than during the height of violence in 2014 and 2015, several Ukrainian army personnel are killed every week. The United Nations estimates that at least 10,000 people have been killed in eastern Ukraine since the start of the conflict in March 2014.

Despite clearly lacking key resources for peace monitoring, the OSCE’s mission is viewed as essential to ending the fighting as prescribed by the 2015 Minsk accords forged by Ukraine, Russia, France, and Germany. As the only third party standing watch along the line of control, the OSCE’s presence serves as a deterrent to major military flare-ups and civilian deaths.

Even so, most of the provisions in the Minsk accords remain unfulfilled, including the complete withdrawal of heavy weapons, a sustained prisoner exchange, and the granting of amnesty for separatists. The OSCE continues to have only limited access to certain separatist regions in the Donbass, and the notion of reinstalling Ukrainian border guards near the Russian border remains fanciful. There is also little progress on the passage of constitutional reforms in Kiev, which would grant autonomy to separatist regions.

A key weakness of the monitoring mission is the daytime work hours kept by OSCE personnel. The hostilities often begin after the monitors pack up and leave for the day. The violence might include a nighttime round of bullets zipping across the pro-Russian side toward a barracks for Ukrainian conscripts or heavy artillery shot from Ukrainian-controlled territory toward rebel targets.

“What they’ve found is that a lot of the cease-fire violations happen at night when the [OSCE] patrols aren’t there,” Daniel Baer, the U.S. ambassador to the OSCE, told FP in an interview.

The long-range drones were crucial for creating a “disincentive for Russian-led separatist forces to launch new attacks at night,” Baer said.

They were also useful for spotting nighttime rail shipments of weapons to rebels and identifying the increasing number of unmarked mines and improvised explosive devices, or IEDs.

“It was clear that this was a systematic Russian effort to limit the capacity of the [OSCE] to see all kinds of things, including the ongoing Russian resupply,” Baer said.

Acknowledging the problem, Rajakovic, the OSCE spokeswoman, said the mission is working on “negotiating a new service contract and is hoping to resume long-range UAV operations as soon as possible.” But it’s unclear when that might happen.

Rajakovic declined to discuss the terms of the previous drone contract, but Baer said the dronemaker Schiebel works as a service provider for the OSCE, charging by flight hours. Because of concerted attempts to shoot down the S-100 drones or electronically jam the aircraft, the service became prohibitively expensive, he said.

“My understanding is if you wanted to go buy [a drone] from the provider that they cost well upwards of a million dollars each, so the expense of a takedown is considerable,” Baer said.

The former senior OSCE official said the Austrian dronemaker proved incapable of operating in a hostile wartime environment.

“I truly believe that Schiebel was out of their depth in this one,” the official said. “Live fire and GPS jamming were the two main factors for the loss of the drones. The units did not have the capabilities to resist jamming. Moreover, winter weather meant that they were grounded days at a time.”

Schiebel may not be the only drone provider wary of going toe-to-toe with hostile adversaries armed with military-grade equipment.

Baer said the OSCE found another drone provider, but the firm “rethought their willingness to provide that service” because of the hostile environment in Ukraine. The firm’s reluctance led to “this gap in the capabilities,” he said.

In the meantime, the OSCE mission continues to operate midrange and mini-UAVs over Ukraine. But they do not have the scope or capabilities that the long-range drones had and that are necessary to cover the most contested areas.

The drone gap isn’t the only logistical snag for monitors.

In a key OSCE mission near the Russian-Ukrainian border, patrols have for several months asked permission to use a rather primitive tool: binoculars. But Russia has categorically refused those requests. In June, frustrated by the lack of cooperation, Britain’s ambassador to the OSCE, Sian MacLeod, took to Twitter to accuse Moscow of preventing the mission from doing its job. “What’s to hide?” she tweeted.

Now, in late October, the personnel seeking a closer look at two key checkpoints still don’t have access to binoculars, prompting growing frustration among Western member states.

“Russia has effectively put blinders on the observer mission,” one Western diplomat said, “curbing its operational effectiveness and providing continued cover for the military personnel, hardware, equipment, and other support it continues to push into Donetsk and Luhansk in blatant violation of the Minsk agreements.”

Reporting for this story was collected in Kiev on a study tour supported by the German Marshall Fund of the United States.